X-ray, i.r., and Raman studies of the anhydrous chlorates and bromates of strontium, barium, and lead - crystal structure of Sr(ClO3)2 and Sr(BrO3)2

Single crystals of the hitherto badly characterized anhydrous halates Sr(ClO3)2, Sr(BrO3)2, Ba(BrO3)2, Pb(ClO3)2, and Pb(BrO3)2 have been obtained by crystallization from an aqueous solution or by heating aqueous suspensions of the corresponding monohydrates to 95, 185, 130, and 105 0C, respectively, in a vacuum. The halates crystallize in the orthorhombic space group Fdd2-C/sub 2v//sup 19/ (Z = 8) with the exception of Sr(BrO3)2, which is distorted to the monoclinic space group Cc-C/sub s//sup 4/ (Z = 4). The crystal structure of Sr(ClO3)2 and Sr(BrO3)2 have been determined using single crystal X-ray diffraction data. In both compounds, distorted SrO8 dodecahedra (bisphenoids) are connected to a four-connected three-dimensional net. The ClO3- ions and one of the two crystallographically non-equivalent BrO3- ions are strongly distorted. The structures of these compounds and those of Ba(IO3)2 and of Ba(ClO3)2 x 1 H2O type compounds are related to a hypothetical AB2 structure with diamond like arrangement of the metal ions of the common super group Fddd-D/sub 2h//sup 4/. The results of i.r. and Raman spectroscopic measurements are reported and discussed in terms of the crystal structures. (author)